Sleeve valve engines display certain limitations, one of which is the shape of the port opening and closing path imposed by a single sleeve crank joined to the trailing end of the sleeve by a ball and socket. The path is elliptical in shape. It is preferable to place the topmost piston ring close to the piston crown to ensure low emissions.
If the stroke of the sleeve crank is made long enough to obtain sufficient sleeve aperture opening then the rotational motion necessitates wide port apertures. During the overlap period in the Otto cycle when both ports apertures are open together and the piston is near Top Dead Centre the piston rings or at least the top ring will cross the port apertures and will not be adequately supported. They tend to “fall in” causing excessive ring wear.
Modern engines need high compression ratios to achieve better engine efficiency and this means that the piston crown is closer to the cylinder head which reduces clearance volume. The end result is that the piston crown further protrudes into the aperture zone.
In our co-pending application for Patent No. 2008901933 we describe a sleeve valve construction wherein the sleeve has an inlet aperture and an outlet aperture and an internal coolant path between the apertures in the wall of the sleeve for conducting the heat of combustion away from the sleeve. This improvement is applicable to sleeves of that particular construction.
In U.S. Pat. No. 2,411,571 a sleeve valve engine with opposed cylinders has a sleeve valve drive which uses a pair of ring gears to rotate the sleeve for each of the cylinders. Axial movement of the sleeve is imparted by a rotating disc adjacent to the sleeves which projects into a helical groove in the end of the sleeve. The pitch and length of the groove is slight so as to cause sufficient reciprocation to rub away carbon deports which would otherwise collect in the sleeve ports. This is not effective for assisting with advantageous port shape.